Acoustic material



COMPosmows,

COATING OR-PLASTIC.

ale

Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE I JOHN H. DELANEY, OF LOS ANGELES, CALIFORNIA; UNION BANK & TRUST CO. OF LOS ANGELES, ADMINISTRATOR OF SAID JOHN H. DELANEY, DECEASED, ASSIGNOB TO ESTATE OF ADA W. DELANEY, DECEASED ACOUSTIC MATERIAL No Drawing. Application filed April 9,

This invention relates to acoustics, and particularly to means whereby the acoustic properties of an interior, such as a church, theatre, or the like, can be improved.

It is well-known that, if no precautions be taken, and when ordinary interior finishes are applied to the walls, such finishes serve as reflectors for sound. The result is that audition is materially interfered with. In order to correct this, it has been proposed to provide a finish that absorbs a large ortion of the incident sound energy, there y pre venting reflection to a large extent. Such a finish can be provided for example, by applying porous or bubbly plaster, especially one in which porous material, such as pumice particles is incorporated.

Such finishes, while capable of use, also have inherent disadvantages. They cannot readily be applied directly by an ordinary hawk and trowel, or else if once applied, they do not cling to the wall surfaces for an indefinite period, but tend to dro off.

It is one of the objects 0 my invention to make it possible to apply such acoustic finishes with an ordinary hawk and trowel, while obviating these disadvantages; and especially by careful choice of the proportioning of the constituents.

In one form of my invention. I utilize a binde Tvith a S111 base T r such as .aster w of Paris or an egulvalent inder, whlcli is homogeneous y mixe with e ervescm or gas evolving material to produce pits, c annels, or grooves, and in which is also included aggregate material, such as sand, orporous material in the form of granules, such as pumice. Due to the spongy character of the binder after it is a plied, it can readily ab- 40 sorb and retain moisture, which deteriorates the materials, and renders the entire finish weak. It is another object of my invention to make it possible to secure the porous effeet, and yet ensure against too great an absorption of moisture.

My invention possesses further advantages and has other ob ects which will be made apparent from the following description of one form of the invention. Although but one form is specifically described, it is of course 1928. Serial No. 268,805.

evident that my invention may be embodied in other forms; and the scope of my invent1on may best be determined by the aid of the claims appended hereto.

In practicing my invention, I utilize three fundamental homogeneously commin led ingredients; a binder such as plaster 0 Paris, 1n the dry form; eifervescing material; and lumps or grains of a e ate such as sand or .orous material, suc as punnce.

I find that by careful proportioning of the aggregate, the efi'ervescing material, and the binder, I obtain a material that can easily be applied and is strong when applied. The best proportioning, I find, is obtained by mixing two cubic feet of laster of Paris or other binder in solid, powdered form to three cubic feet of the a re ate material; and to this mixture I add equal amounts of aluminum sulfate and calcium carbonate ese materials produce eflervescence anT the preferred amount is four and three quarter pounds of each of these salts added to the mixture of aggregate and the binder. The proportion of ag regat-e and binder can be varied slightly; or example, it is possible to utilize one cubic foot of the binder to four of the porous material; this is the lower limit for the binder; the upper limit is reached when three cubic feet of binder is mixed with two of aggregate.

The addition of the effervescing material is of great benefit. In the first place, when water is added to the mixture as specified, the bubbling serves to agitate the aggregate particles and the binder, and thereby to produce a homogeneous spongy texture. In addition to this advantage, I find that the resultant spongy material is much more cohesive than if no effervescing material were present, and the mixture exhibits more strength. It is for this reason that I can use as poor a mixture of binder and aggregate as one to four without materially weakening the finish.

The combination of aluminum sulphate and calcium carbonate as the elfervescing material is also advantageous because it has the property of absorbing moisture; that is, it

Examiner with this combination, it can stay fresh a long time, because moisture accumulating in the mixture will cause no hardening, but will instead be absorbed by the hygroscopic ma- 5 terial.

When the wet mixture is placed on the walls as described, the pits and channels formed by the eifervescing material are left in the finish, and it therefore has a high sound absorbing effect. The addition of porous material, such as pumice instead of sand or other aggregate, renders the finish still more eificient for sound absorption. Furthermore, the finish after it is applied,

resists moisture because of the residual hygroscopic material retained therein.

Of course it is possible to utilize other form of binder instead of plaster of Paris; for example, the various forms of cements could be used, as well as other cemen s us1n a gypsum base. Also, other forms of porous miattpr insteadlof piliimieeffould be substitute or examp e co e. owever, pumice is preferred because its color even if exposed in 25. the finish is unobjectionable. It can be utilized in small sizes; for example, ranging from such that will pass a sixteenth inch mesh, to such that will pass a half inch mesh.

I claim:

1. Material adapted to be used for the finish of wall surfaces, comprising not more than three parts by volume of a binder free from water, to two parts by volume of aggregate; and not less than one part by volume of the binder to four parts by volume of the aggregate; and efli'ervescing matter suiiicient to impart a spongy texture to the material when wetted.

2. Material adapted to be used for the fin- 40 ish of wall surfaces, comprising not more than three parts by volume of calcined gypsum, to two parts by volume of aggregate; and not less than one part by volume of the gypsum to four parts by volume of the aggregate; and efi'ervescing matter sufiicient to impart a spongy texture to the material when wetted.

3. The material as specified in claim 1, in which the efi'ervescing matter includes equal parts of aluminum sulphate and calcium carbonate, in the proportion of about 4% pounds of each to five cubic feet of the binder and aggregate.

In testimony whereof I have hereunto set my hand.

JOHN H. DELANEY. 

